Using air guns for cleaning stony surfaces, wooden handmade articles, or items of the historical or modern architecture made of natural or artificial materials has been known for a while. Such guns spray a fluid, generally air or air mixed with abrasive powders, on the surface to be cleaned so as to remove the undesired stratifications and deposits, such as, for example, graffiti.
A problem which occurs when using such guns stands in the fact that, spraying a fluid through a direct jet, the power of such jet is difficult to dose and often results too weak, performing an insufficient cleaning of the wall to be cleaned, or otherwise results too powerful, performing a cleaning which is not very selective and triggering an alteration of the surface to be cleaned. To overcome such a problem, is also known the use of vortex generator air guns, suitable to spray the fluid through a jet having a helical motion.
As an example, U.S. Pat. No. 6,050,504 discloses a spray dispensing device which comprises passageways for directing streams of air and liquid, where the liquid is broken up into droplets and emitted as a fine spray through an orifice. An annular air passageway is arranged concentrically disposed around a liquid passageway. The air is led through swirl-shaped passages, where a rotary motion is imparted to the annular air stream.
Patent application JP 4145229 shows a vortex flow generator for a gas, wherein a high pressure air stream is injected into a gas stream. The high pressure air stream is inclined at a constant angle with respect to the axis of gas stream, and is jetted from a direction focused out of the axis of the gas stream. The velocity of high pressure air is therefore provided with a vector component in the direction of the axis of the gas flow, and with a vector component in the direction intersecting the gas flow, so that the air is emitted with a turning effect, forming a vortex. Nevertheless such a vortex flow generator is not suited to be arranged in a gun, but in the supply device to which the gun is connected.
The proposed solutions do not form practical applications for the users, because they turn out to be complicated to assemble, or because they perform the formation of the vortex before the air enters the gun, thus determining the at least partial loss of the vortex effect when the fluid is sprayed.
Utility model CN 2332492 Y shows an air gun comprising an electrostatic pipe, an inner shaft, an outer sleeve, a dual flow distribution assembly, a fixed seat and a spray head suitable to spray a mixture of air and powder. The electrostatic pipe is provided with a flow distribution groove whose inner surface presents a spiral concave shape, such that the vortex air stream, quickly turning, moves the flow distribution groove, and causes the flow distribution groove to be rubbed with the wall of the electrostatic pipe. Such a rubbing makes the outer wall of the inner shaft generate electricity which modifies the electrostatic charge of the powder in a way as to improve the coating effect. Yet, such a device has a scarce efficiency in that it gives a rotary motion only to a part of the fluid which crosses it.